FIELD OF THE INVENTION
This invention relates in general to the insufflating of gas to a human or animal body and in particular to a new and useful method device for controlling the flow of insufflating gas.
In a device previously known from German Pat. No. 34 13 631 of this kind, two fixedly preset pressure reducers are provided, which give the gas pressure, for example, preset to 50 mmHg. A succeeding throughflow regulator controls the stream in the gas line, for example, to 11/min. The gas flow through a magnetic valve into a throughflow meter, with the pressure drop occurring here as a consequence of frictional resistance being kept constant by the throughflow regualator. The pressure decrease serves at the same time for throughflow regualtion in the throughflow regulator. Subsequently, the gas streams through an optic throughflow indicating device, before streaming into the insufflation instrument. Immediately in front of it, the pressure meter is connected to the gas line. The known device comprises further, in addition to the main gas line, a branch line, which connects the though flow regualtor with the optic throughflow indicator via a magnetic valve. Both magnetic valves, the pressuremeter unit and the throughflow meter are connected to an electronic evaluating and control circuit, which is provided with an indicating device for total pressure, the intra-abdominal static pressure, the gas flow velocity and the total consumed gas quantity.
The known device, because of the large number of structural elements is elaborate and expensive to produce. Moreover, the two throughflow meters respectively throughflow regulators and the optic throughflow indicator are located in the gas line, by which interferences are created, in particular considerable resistances in the gas stream. Lastly, the process to be carried out with this device of measuring pressure and regulating flow is very complicated. First, on switching on the device, the stream resistance of the entire line system has to be determined, the resistance pressure has to be subtracted from the currently measured pressure at the measuring unit for the determination of the intra-abdominal static pressure. The difference of the two pressure valves gives the ultra-abdominal static pressure. Moreover, at reaching a preseelected nominal pressure, the gas flow is stopped automatically by the electronic control circuit, in the process of which the main gas line leading through the throughflow meter is closed and the branch line opened synchronously. The pressure value at the throughflow regulator is retained. On reaching the preset nominal pressure, the current measured throughflow value is stored in the electronic control circuit and used for determining the intra-abdominal pressure according to a formula in which several measuring parameters are substituted. This determination of the intra-abdominal pressure over flow size and back up pressure at the device output is most uncertain at small pressures and great flow. This, however, is exactly the most common situation in the normal application of this device.